260 MORPHOLOGY AND EVOLUTION thyro-hyoid muscle is as in Man. The crico-thyroid muscle is not fan-shaped as in Man; it runs from the lower and outer part of the cricoid cartilage to the lower border of the thyroid cartilage. The posterior crico-arytenoid muscle runs from the posterior cricoid lamina to the arytenoidal processus muscularis; whence the lateral muscle runs to the lateral part of the cricoid arch. The thyro-arytenoid muscle runs from the lower half of the inner surface of the thyroid ala, near the ^middle plane, to the outer border of the arytenoid cartilage above the crico-arytenoideus; it does not divide as in Man. The transverse arytenoid muscle is stronger than the oblique one. In the Gorilla the thyro-arytenoid muscle is as in Man, and the oblique arytenoid is stronger than the transverse arytenoid muscle. The Orang has no oblique band. Interior of the Larynx.*—In the Chimpanzee the aryteno-epiglottic folds are small. The true vocal cords are soft, being composed mainly of mucous membrane and elastic tissue. The false cords are soft, and the ventricles are well marked ; they communicate with the air-sac through the thyro-hyoid membrane. Posteriorly the cuneiform tubercles are close together. The pyriform sinus is better marked than in Man. The upper division of the larynx is shallow, the middle division is larger than, and the lower division is similar to, that in Man. In the Gorilla, according to Duckworth (50), the plica vocalis is less like that of Man than is that of the Chimpanzee. Its free margin has an attenuated membranous flange and no isolated muscle fibres are present. * Accounts of the larynx and its muscles have been given in papers 53. <Sp» IM, 162, I99» 201, 259, 330, 357» 399» 4Oi» 411.